On Wednesday 16 January 2008 22:39, Matthew Garrett wrote:
> Vendors often ship machines with a choice of integrated or discrete
> graphics, and use the same DSDT for both. As a result, the ACPI video
> module will locate devices that may not exist on this specific platform.
> Attempt to determine whether the device exists or not, and abort the
> device creation if it doesn't.
>
> Signed-off-by: Matthew Garrett <mjg59@xxxxxxxxxxxxx>
>
> ---
>
> I'm still not convinced that this can be done reliably, especially if
> anyone ever produces ACPI devices that aren't PCI-based. On the other
> hand, I believe that this will work correctly (ie, discard devices for
> integrated hardware if discrete hardware is present, and vice-versa) in
> all existing cases. The most irritating feature is that there's no good
> way to determine if an _ADR method refers to a PCI device or not - 0x00
> could mean the PCI host bridge or the first video device hanging off an
> AGP bridge. So far all the implementations I've seen use low numbers for
> devices that aren't directly on the root PCI bus, so I've just assumed
> that they'll always be less than 0x10000. If someone puts a graphics
> core in their host bridge, this will break. But that would seem a mad
> thing to do, so I'm going to pretend it's impossible.
>
> diff --git a/drivers/acpi/video.c b/drivers/acpi/video.c
> index 12b2adb..1906eff 100644
> --- a/drivers/acpi/video.c
> +++ b/drivers/acpi/video.c
> @@ -1266,8 +1266,37 @@ acpi_video_bus_write_DOS(struct file *file,
>
> static int acpi_video_bus_add_fs(struct acpi_device *device)
> {
> + long device_id;
> + int status;
> struct proc_dir_entry *entry = NULL;
> struct acpi_video_bus *video;
> + struct device *dev;
> +
> + status =
> + acpi_evaluate_integer(device->handle, "_ADR", NULL, &device_id);
> +
> + if (!ACPI_SUCCESS(status))
> + return -ENODEV;
> +
> + /* We need to attempt to determine whether the _ADR refers to a
> + PCI device or not. There's no terribly good way to do this,
> + so the best we can hope for is to assume that there'll never
> + be a video device in the host bridge */
_ADR returns a bus-specific format.
In the case of a video device, section B.6.1 says that
_ADR returns a 32-bit device ID, and that
it is the same number as returned in the _DOD list.
That is the only constraint.
So I don't think you can use the numerical value returned
to have any particular meaning at all.
In particular, comparing it to magic number 0x10000 makes no sense.
-Len
> + if (device_id >= 0x10000) {
> + /* It looks like a PCI device. Does it exist? */
> + dev = acpi_get_physical_device(device->handle);
> + } else {
> + /* It doesn't look like a PCI device. Does its parent
> + exist? */
> + acpi_handle phandle;
> + if (acpi_get_parent(device->handle, &phandle))
> + return -ENODEV;
> + dev = acpi_get_physical_device(phandle);
> + }
> + if (!dev)
> + return -ENODEV;
> + put_device(dev);
> +
>
>
> video = acpi_driver_data(device);
>
-
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